What's your evidence that the murder was premeditated though? As far as we know he didn't even look into how to cover it up until afterwards.

All the known facts are congurent with someone who acted in the heat of the moment and then tried to get the best result for himself considering the very bad situation he got himself in. Trying to cover up the act and mislead the court is certainly not very ethical but it is a far cry from the murder itself being premeditated.